cppcheck/lib/checkassignif.cpp

/*
 * Cppcheck - A tool for static C/C++ code analysis
 * Copyright (C) 2007-2011 Daniel Marjamäki and Cppcheck team.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

//---------------------------------------------------------------------------
// Check for assignment / condition mismatches
//---------------------------------------------------------------------------

#include "checkassignif.h"
#include "symboldatabase.h"

//---------------------------------------------------------------------------

// Register this check class (by creating a static instance of it)
namespace
{
CheckAssignIf instance;
}


void CheckAssignIf::assignIf()
{
    if (!_settings->_checkCodingStyle)
        return;

    for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next())
    {
        if (tok->str() != "=")
            continue;

        if (Token::Match(tok->tokAt(-2), "[;{}] %var% = %var% & %num% ;"))
        {
            const unsigned int varid(tok->previous()->varId());
            if (varid == 0)
                continue;

            const MathLib::bigint num = MathLib::toLongNumber(tok->strAt(3));
            if (num < 0)
                continue;

            for (const Token *tok2 = tok->tokAt(4); tok2; tok2 = tok2->next())
            {
                if (tok2->str() == "(" || tok2->str() == "}" || tok2->str() == "=")
                    break;
                if (Token::Match(tok2,"if ( %varid% %any% %num% &&|%oror%|)", varid))
                {
                    const std::string op(tok2->strAt(3));
                    const MathLib::bigint num2 = MathLib::toLongNumber(tok2->strAt(4));
                    if (op == "==" && (num & num2) != num2)
                        assignIfError(tok2, false);
                    else if (op == "!=" && (num & num2) != num2)
                        assignIfError(tok2, true);
                    break;
                }
            }
        }
    }
}

void CheckAssignIf::assignIfError(const Token *tok, bool result)
{
    reportError(tok, Severity::style,
                "assignIfError",
                "Mismatching assignment and comparison, comparison is always " + std::string(result ? "true" : "false"));
}





void CheckAssignIf::comparison()
{
    if (!_settings->_checkCodingStyle)
        return;

    for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next())
    {
        if (tok->str() != "&")
            continue;

        if (Token::Match(tok, "& %num% )| ==|!= %num% &&|%oror%|)"))
        {
            const MathLib::bigint num1 = MathLib::toLongNumber(tok->strAt(1));
            if (num1 < 0)
                continue;

            const Token *compareToken = tok->tokAt(2);
            if (compareToken->str() == ")")
            {
                if (!Token::Match(compareToken->link()->previous(), "(|%oror%|&&"))
                    continue;
                compareToken = compareToken->next();
            }

            const MathLib::bigint num2 = MathLib::toLongNumber(compareToken->strAt(1));
            if (num2 < 0)
                continue;

            if ((num1 & num2) != num2)
            {
                const std::string op(compareToken->str());
                comparisonError(tok, op=="==" ? false : true);
            }
        }
    }
}

void CheckAssignIf::comparisonError(const Token *tok, bool result)
{
    std::string errmsg("Mismatching comparison, the result is always " + std::string(result ? "true" : "false") + "\n"
                       "Mismatching comparison. This error message is for example given for such a comparison: ");

    if (result)
        errmsg += "'(x & 6 != 1)'. The result of 'x & 6' can't be 1 so the result of the comparison is always true";
    else
        errmsg += "'(x & 6 == 1)'. The result of 'x & 6' can't be 1 so the result of the comparison is always false";


    reportError(tok, Severity::style, "comparisonError", errmsg);
}






void CheckAssignIf::multicompare()
{
    if (!_settings->_checkCodingStyle)
        return;

    for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next())
    {
        if (Token::Match(tok, "if ( %var% & %num% ) {"))
        {
            const unsigned int varid(tok->tokAt(2)->varId());
            if (varid == 0)
                continue;

            const MathLib::bigint num1 = MathLib::toLongNumber(tok->strAt(4));
            if (num1 < 0)
                continue;

            const Token *tok2 = tok->tokAt(6)->link();
            while (Token::simpleMatch(tok2, "} else { if ("))
            {
                // Goto '('
                const Token * const opar = tok2->tokAt(4);

                // tok2: skip if-block
                tok2 = opar->link();
                if (Token::simpleMatch(tok2, ") {"))
                    tok2 = tok2->next()->link();

                // check condition..
                if (Token::Match(opar, "( %varid% == %num% &&|%oror%|)", varid))
                {
                    const MathLib::bigint num2 = MathLib::toLongNumber(opar->strAt(3));
                    if (num2 < 0)
                        continue;

                    if ((num1 & num2) == num2)
                    {
                        multicompareError(opar, tok->linenr());
                    }
                }
            }
        }
    }
}

void CheckAssignIf::multicompareError(const Token *tok, unsigned int line1)
{
    std::ostringstream errmsg;
    errmsg << "Comparison is always false because otherwise the condition at line "
           << line1
           << " is not false";

    reportError(tok, Severity::style, "multicompare", errmsg.str());
}